The overall objective of this proposal is to design, develop a new cell separating technique that will provide a much more rapid and improved separation of cell populations including peripheral blood, bone marrow. In Phase I, the applicant organization (Technical Research Associates, Inc., TRA) has built and tested a device which rapidly separates bone marrow cells by size using patented pseudo-standing wave ultrasound technologies. Instead of sedimenting cells in a gravitation field, the technique used an acoustic velocity gradient to levitate the cells up through a column of fluid. The inverted column eliminated the traditional problem of "streaming limit" associated with unit gravity sedimentation and required no tedious density gradient formation. The apparatus is simple with no moving parts. Acoustic Velocity Gradient Fractionation provides a unique method which potentially discriminates between cells not only on the basis of size and shape but by differences in internal structure. This technology, when perfected, could provide a rapid and efficient fractionation of various cell populations including peripheral blood and bone marrow.